The notes (and exercise) distinguish between real and implied triangles: real triangles have clearly definable edges; implied triangles where the eye detects the shape as result of three well-defined points creating implied lines.
The first task is to find a triangular shape:
This is the rear badge on my wife's Mitsubishi Colt. The reflection of the sky in the badge adds some interest and increases the contrast from the background. Of course it could be argued that this is an implied rather than real triangle as the edges are not truly joined (and there are several implied triangles within the shape) but I think the basic structure is clear enough.
The next task was to create a triangle by perspective converging to the top of the frame. I decided to add the opportunity to experiment with a technique that I had not done before: using slow shutter speeds to make lines from head and tail lights of vehicles. I set up a tripod on a bridge over the A4174 ring road east of Bristol and got the above image.This image was taken at 4.0 second shutter speed, obtaining a good run of lighting and also meant that f8.0 aperture could be used, allowing a reasonable depth of field.
The triangular prespective is achieved by the road lighting but the head and tail lights emphasise the shape and add interest.
An inverted triangle by perspective was more difficult to locate. I found two examples that have used here. The first is an uninteresting image of a canopy, the second is a leaf from interior plant, the veins providing clear lines leading downwards.
The second part of the exercise was to demonstrate implied triangles using still life, ideally five or six objects.
With some encouragement, I managed to get six satsumas to stack into a classic 3-2-1 format to demonstrate a triangle whose apex is at the top of the image. I used blue crepe paper as background as orange and blue are classically viewed as harmonious colours (see p94 The Photographer's Mind by Michael Freeman). There was sufficient natural light but the addition of flash from an off camera Speedlite 430 to the right balanced the lighting and reduced shadow.
An inverted triangle was created by setting up three apples (stability with six apples was impossible to achieve) and placing on green crepe paper (again the harmonious colours). Some carefully placed Blu tack helped to stabilise the base and the top apples were anchored by using needles. Off camera flash was used as for the image above.
The inverted triangle looks unstable; our natural instinct is that a top heavy structure is unbalanced. I find the image difficult to look at for long because of this.
The image below was taken of three people so as to show their faces in a triangle:
It is a scalene triangle on account of the relative heights but demonstrates the point.
One can look back at other images taken for different reasons to see real and implied triangles. Here are some examples from the first part of the course:
And some more recent examples taken from this part of the course:
